1. Field of the Invention
The present invention relates to die bonding equipment and methods for the fabrication of ball grid packages and more particularly to a die bonding method capable of detecting a failure of a land pattern on a mount tape before a chip transfer unit picks up a chip and capable of matching a good land pattern to a good semiconductor chip and a failed land pattern to a failed semiconductor chip.
2. Description of the Related Art
Recently, technologies for packaging semiconductor chips have rapidly developed with the development of thin film forming technologies. Ball grid array packages, currently in use, are a result of the application of such technologies. A ball grid array package uses a flexible tape in place of a lead frame. The flexible tape includes a conductive pattern formed thereon. One end of the conductive pattern is soldered to terminals of a printed circuit board by a solder ball interposed therebetween, and the other end is bonded to bonding pads that act as input and output terminals of a semiconductor chip.
In the fabrication of ball grid array packages, the process of attaching solder balls is the last step, which provides various advantages in carriage and handling of elements for a die attaching process and in mass production. Ball grid array packages also make unnecessary the trimming and forming processes that are indispensable in fabrication of more conventional packages.
Recently developed chip scale packages have a fine pitch in which the pitch of solder balls ranges from a few tens of microns to a few hundreds of microns and sizes of such packages approach about 120% of the chip sizes.
To form a fine pitch ball grid package, multiple land patterns are first formed on a rectangular, polyimide based tape. Throughholes are formed at selected portions of the polyimide based tape. The land patterns include solder ball pads, which are on a first surface of the polyimide based tape such that each of the pads covers a corresponding throughhole and has a circular plate shape. The land patterns also include conductive patterns that electrically connect to respective solder ball pads and extend to edges of the tape.
Beam leads, that is, the ends of the conductive patterns, are die-bonded to respective bonding pads of semiconductor chip. For such die bonding, rectangular openings or windows are formed at edges of the polyimide based tape. After the die bonding, an electrical test determines whether or not the land patterns have open or short failures and from the electrical test, failed land patterns are marked. An elastomer is attached to a second surface of the polyimide based tape.
Continuously, the polyimide based tape on which the elastomer is attached is rolled, and the rolled tape is cut to length, for example, to include a number of land patterns. Hereinafter, a rolled tape having the above mentioned unit length is referred to as one base mount tape. A base mount tape""s edge portions are attached to a square mount tape frame using an adhesive tape.
Semiconductor chips separated by sawing a wafer are transferred to corresponding base mount tapes, and a press head die bonds bonding pads of each of the semiconductor chips with beam leads exposed through open windows of base mount tape.
Afterwards, base mount tapes having semiconductor chips attached are subject to a solder ball attaching process. The solder ball attaching process attaches solder balls to solder ball pads through the throughholes in the base mount tape. The above solder ball attaching process prepares multiple ball grid array packages having a fine pitch. The multiple ball grid array packages are separated into individual ball grid array packages, and the individual ball grid array packages are tested. Thus, the above processes fabricate ball grid array packages.
FIG. 1 shows conventional die bonding equipment 100 for fabrication of ball grid array packages having a fine pitch. Referring to FIG. 1, die bonding equipment 100 generally includes a wafer mount frame stocker 5, a base mount stocker 10, a chip pickup table 15, and a bonding unit 20 on a support plate 1. A chip transfer unit 25 moves a semiconductor chip from the chip pickup table 15 to the bonding unit 20, and a guide rail unit 40 guides a base mount tape frame 35 from the base mount tape stocker 10 to the bonding unit 20. Multiple charge coupled device(CCD) cameras observe the operation of die bonding equipment 100.
In FIG. 1, the chip pickup table 15 faces an opening 50 of the wafer mount frame stocker 5 so that a wafer mount frame 45 carrying multiple semiconductor chips can be loaded into or unloaded from the wafer mount frame stocker 5. A square chip tray 55 that is attached to the chip pickup table 15 receives failed semiconductor chips. The chip tray 55 moves together with the chip pickup table 15 in an X-Y plane.
Meanwhile, an alignment table 65, which includes a mount head 60, is spaced apart from the chip pickup table 15. The mount head 60 receives a semiconductor chip from the chip pickup table 15, moves the received semiconductor chip to the bonding unit 20, and aligns the semiconductor chip for die bonding. To align the semiconductor chip, the alignment table 65 can freely move along X-Y coordinate axes as does the chip pickup table 15, and when the semiconductor chip is skewed from the required orientation for bonding of the chip, the alignment table 65 rotates the skewed semiconductor chip for the required alignment. The alignment table 65 can also move along the Z coordinate axis direction.
Here, the chip transfer unit 25, which reciprocates between the chip pickup table 15 and the alignment table 65, transfers semiconductor chips from the wafer mount frame 45 of the chip pickup table 15. The chip transfer unit 25 includes: a collet 70 (hereinafter referred to as the first collet) for holding good semiconductor chips with a vacuum; a collet 75 (hereinafter referred to as the second collet) for holding failed semiconductor chips; and a moving block 80 including a collet selection unit (not shown) that selects the first or second collet 70 or 75 for use. The chip transfer unit 25 also includes a straight line reciprocating unit (not shown) for transferring the moving block 80.
The described base mount tape stocker 10 is spaced away from the wafer mount frame stocker 5. The guide rail unit 40 extends from an opening 85 of the base mount tape stocker 10, and a base mount tape frame 35 received at the base mount tape stocker 10 is unloaded through the opening 85. The guide rail unit 40 includes a pair of guide rails 42 and 44 that guide the base mount tape frame 35. Each of the guide rails has a moving unit (not shown) for moving the base mount tape frame 35, which is unloaded from the base mount tape stocker 10.
A bonding unit 20 is over the guide rails 42 and 44 and distant from the base mount tape stocker 10. The bonding unit 20 includes a press head 22, which moves up and down, and a bonding unit CCD camera 24, which moves together with the press head 22. The press head 22 is over the base mount tape frame 35, and the mount head 60 is below the base mount tape frame 35 so that the press head 22 faces the mount head 60. The bonding unit CCD camera 24 checks the position of the base mount tape frame 35 as it moves and simultaneously checks for a failed mark formed during the production of the base mount tape.
In addition to the bonding unit CCD camera 24, the conventional die bonding equipment typically includes two other CCD cameras. A chip pickup table CCD camera 17 is for determining a position of a failed semiconductor chip or a good semiconductor chip among the chips sawed from a wafer, and an alignment table CCD camera 62 is for checking the alignment of a semiconductor chip on the mount head 60 of the alignment table 65.
Hereinafter, the operation of the conventional die bonding equipment is described with reference to FIG. 1.
First, prior to starting the die bonding process, an operator discriminates failed semiconductor chips from a sawed wafer mounted on the wafer mount frame 45 and manually loads the discriminated failed semiconductor chips into the failed semiconductor chip tray 55. This avoids an increase in the loading time for loading of failed semiconductor chips. Such increases in the loading time occur when another wafer is loaded to start a process after processing of a wafer is completed, a corresponding land pattern to be bonded among base mount tapes is failed, and there are no failed semiconductor chips on the wafer mount frame 45.
The operator loads all failed semiconductor chips in the failed semiconductor chip tray 55, and then an unloading unit unloads one sheet of wafer mount frame 45 from the wafer mount frame stocker 5 and fixes the sheet to the chip pickup table 15.
The chip pickup table CCD camera 17 continuously images semiconductor chips on the chip pickup table 15 to discriminate between good semiconductor chips and defective semiconductor chips.
An X-Y table moves the chip pickup table 15 so that a good semiconductor chip is below the first collet 70 of the chip transfer unit 25. To shorten the bonding time, the first collet 70 picks up and stands by with a good semiconductor chip.
Concurrently with the stand by of the first collet 70, the mount tape frame 35 is unloaded from the mount tape stocker 10 and moves to the bonding unit 20 along the guide rail unit 40. At this time, the bonding unit CCD camera 24 of the press head 22 photographs a first land pattern that is being processed first, to thereby discriminate whether the first land pattern is good or defective.
Here, when the first land pattern is good, the good semiconductor chip held by the first collet 70 is moved onto the mount head 60 of the chip alignment table 65 and is then aligned. Thereafter, the aligned good semiconductor chip is transferred onto a corresponding good land pattern of the base mount tape 30 by the movement of the mount head 60. After the transfer of the good chip, the press head 22 moves downward and the mount head 60 moves upward, so that bonding pads of the good semiconductor chip are bonded to beam leads of the good land pattern.
Meanwhile, when the first land pattern as discriminated is defective, the good semiconductor chip held by the first collet 70 returns to an original position. Then, the second collet 75 instead of the first collet 70 picks up the defective semiconductor chip and moves the defective chip onto the mount head 60. Thereafter, the defective chip is transferred to a corresponding defective land pattern of the base mount tape 30 by the movement of the mount head 60 without a specific alignment. After the transfer of the defective chip, the press head 22 moves downward and the mount head 60 moves upward, so that bonding pads of the defective semiconductor chip are bonded to beam leads of the defective land pattern.
The conventional die bonding equipment and method have the following problems.
First, when a land pattern of the base mount tape to be die bonded is determined to be defective, the first collet 70 of the chip transfer unit 25 holds the good semiconductor chip. Therefore, the first collet 70 returns the good semiconductor chip to an original position. Instead of the first collet 70, the second collet 75 holds a defective semiconductor chip on the mount head. Accordingly, a delay occurs.
Second, the bonding unit CCD camera determines whether the land pattern of the base mount tape is good or not during the die bonding time. Accordingly, much time is spent in determining the status of the semiconductor chip.
Third, an operator must manually pick up a defective semiconductor chip from the wafer mount frame and then load the defective semiconductor chip in tray 55. As a result, loading times lengthen.
Fourth, when a use of a defective semiconductor chip that is received in the defective semiconductor tray is required, X-Y table has to move the semiconductor chip tray below the second collet 75. As a result, the time spent in picking up the received defective semiconductor chips increases.
It is therefore an object of the present invention to decrease the die bonding time of a ball grid array package having a fine pitch by determining whether a corresponding land pattern of the base mount tape on which a semiconductor chip is being die-bonded, is good or not before a chip transfer unit picks up a semiconductor chip and thereby allowing the chip transfer unit to pick up a semiconductor chip matching the land pattern.
It is another object of the present invention to shorten a time taken in determining whether a land pattern of a base mount tape is good by performing such a determination only once during the loading of the mount tape.
It is yet another object of the present invention to decrease a time taken in picking up defective semiconductor chips by establishing the defective semiconductor chip tray at the lower face of the collet of the semiconductor chip transfer unit along the trace of the collet and thereby allowing wafer extend table not to be moved in order to pick up a defective semiconductor chip.
It is yet another object of the present invention to shorten the time taken in loading defective semiconductor chips into the defective semiconductor chip tray by allowing the collet of semiconductor chip transfer to perform the work for loading defective semiconductor chips into the defective semiconductor chip tray.
Other objects and advantages of the present invention will be more apparent in view of the description that follows.
One embodiment of the present invention is a die bonding method for a fine pitch ball grid array package. The die bonding method includes inspecting the status and position of a semiconductor chip which is on a mount frame and the status and position of a land pattern of a mount tape, wherein the land pattern is on one surface of the mount tape and the other surface of the mount tape is attached to a surface of the mount frame. Thereafter, the status data and the position data corresponding to the semiconductor chip and the land pattern inspected are stored. After repeating the inspection of one or more semiconductor chips, a semiconductor chip is selected using the stored status data and the position data of the semiconductor chip and the land pattern. The selected semiconductor chip has a status matching to the status of the land pattern at a bonding region for the die bonding. The selected chip is transferred to an alignment region for an operation corresponding to the status of the transferred chip.
Another embodiment of the invention is a die bonding equipment for fine pitch ball grid array packages. The die bonding equipment includes: a semiconductor chip pickup stage for inspecting the status and position of a loaded semiconductor chip, wherein a wafer mount frame is unloaded from a wafer mount frame stocker and the wafer mount frame is loaded on the semiconductor chip pickup stage; an alignment stage spaced apart from the semiconductor chip pickup stage; a chip transfer unit for transferring the semiconductor chip from the semiconductor chip pickup stage to the alignment stage; a guide rail for a mount tape frame having a mount tape on which at least one land pattern is formed, the mount tape frame being transferred from a mount tape frame stocker in which the mount tape frame is received to a die bonding position adjacent to the alignment stage; an inspection system disposed over the guide rail, for inspecting a status and a position of the land pattern on the mount tape frame; and a bonding unit for bonding the land pattern to the semiconductor chip that is mounted on the mount head.